Real-Time Detection for Scattering Scanning Near-Field Optical Microscopy

Date The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline. Thesis directed by Professor Markus Raschke Scattering scanning near-field optical microscopy (s-SNOM) is a powerful technique for measuring spectroscopic properties of materials with spatial resolution previously unobtainable due to the diffraction limit. s-SNOM combines scanning probe microscopy (SPM) with spectroscopy to provide sub-diffraction limited spatial resolution information about optical and related properties of matter. Discriminating the weak elastic s-SNOM signal from various undesirable background signals is critical to the success of s-SNOM as a measurement technique. Traditionally this discrimination is achieved through lock-in detection, in which the s-SNOM signal is restricted to, and measured at harmonics of an atomic force microscope tip oscillation frequency Ω. However, this detection technique neglects information at all undetected harmonics. To overcome this loss of information, for my honors thesis, I developed a new s-SNOM detection scheme based upon the real-time acquisition of the s-SNOM signal to ensure no information is lost. With this new detection scheme I have been able to simulate gated detection elastic s-SNOM –a measurement which has not yet been realized experimentally– and determine that it provides no more than background-ridden information readily obtainable with lock-in detection. I have also been able to generate, for the first time, an experimental reconstruction of the distance dependence of the tip-sample interaction for elastic s-SNOM measurements and compare it to theoretical models. Acknowledgements I would like to thank Prof. Markus Raschke for providing me with many outstanding opportunities to begin to form my identity as a researcher. These opportunities have included everything from learning the basics of using lab equipment to traveling to Germany for a collaborative project. The skill and experience I've gained under his guidance have prepared me very well for what lies ahead in my career as a researcher. I would like to particularly thank Sam Berweger for mentoring me in and out of the lab. Following his example has helped me to develop an intuition for experimental physics I never could have learned in a classroom. His guidance on this project has helped me make the transition from fumbling around in the lab figuring out how everything works to pulling all of my experience together to produce results. It has been a great pleasure working …